Differential sensitivity of infectious and defective-interfering particles of sindbis virus to ultraviolet irradiation

Abstract

A quantitative assay for defective-interfering (DI) particles of Sindbis virus (SV) was developed and shown to have an efficiency comparable to that of the plaque assay for infective virus. The assay was used to quantitate the kinetics of ultraviolet inactivation of the interfering activity of DI particles. For SV BP19 (a virus stock produced by 19 serial undiluted passages in BHK cells) and SV A17 (produced by 7 serial undiluted passages in A. albopictus cells) the interfering activity was seven- and twofold, respectively, more resistant to inactivation by uv light than was infectivity. For the DI particles in SV BP19 the uv target size correlated very well with the size of the DI genome RNA (MW = 0.59 and 0.63 × 10 6) but for the DI particles in SV AP7 the uv target size was 25–30% smaller than the DI genome (MW = 3.2 × 10 6). These results suggest that the entire genome of the DI particle in SV AP7 may not be required for interference. In contrast to the results obtained with DI particles, the interfering capacity of a nondefective ts mutant was almost as sensitive to inactivation as was infectivity.